Syntax Format(s): The U3D run-time architecture may be extended by new objects not defined in this document. These new objects shall be in the class of modifier objects within a modifier chain. File format

requirements for the new objects are in 9.4.6 New Object Type and 9.4.7 New Object Block [[6]]

Description: This Standard defines the syntax and semantics of the Universal 3D file format, an extensible format for downstream 3D CAD repurposing and visualization, useful for many mainstream business applications. Salient features of the U3D file format described in this document include: execution architecture that facilitates optimal run-time modification of geometry, continuous-level-of-detail, domain-specific compression, progressive data streaming and playback, free-form surfaces, key-frame and bones-based animation, and extensibility of U3D format and run-time.

The U3D file format specification does not address issues regarding reliability of the transport layer or communications channel. It is assumed that reliability issues will be addressed by a different protocol layer.

The U3D file format specification does not address run-time extensibility of an implementation of the U3D architecture. [[7]]

History:

In 2004, Ecma International formed Technical Committee 43 (TC43) to specify Universal 3D (U3D) File Format specification. The Universal 3D File Format specification is primarily intended for downstream 3D CAD repurposing and visualization purposes. The 1st Edition of the U3D File Format was adopted by the General Assembly of December 2004.

In 2005, TC43 added file format extensibility to the 2nd Edition of the U3D File Format specification. The 2nd Edition of the U3D File Format was submitted to ISO/IEC for fast-track processing.

In 2006, changes were made as a result of comments received during the ISO/IEC DIS ballot process.

In 2007, TC43 added the Free-Form Curve and Surface Extension to the 4th Edition of the U3D File Format specification that adds support for Uniform and Non-Uniform, Rational and Non-Rational Free-Form Curves and

Magic numbers: The first block is the File Header Block. The File Header Block is the only required block for a U3D file. The File Header Block is followed by declaration blocks. Contains the string U3D at the begining of the file.

Adoption: The goal is a universal standard for three-dimensional data of all kinds, to facilitate data exchange. The consortium promoted also the development of an open source library for facilitating the adoption of the format. The format is natively supported by the PDF format and 3D objects in U3D format can be inserted into PDF documents and interactively visualized by Acrobat Reader (since version 7).

Licensing and patent claims: N/A

Typical use: CAD

File classification:

Type {Binary, Text}: Both

Raster data:

Raster data 2D:

Is Supported:False

Description: N/A

Raster data 3D:

Is Supported: False

Description: N/A

Geometric representation:

Implicit representation:

Implicit surfaces:

Is Supported: False

Description: N/A

Implicit curves:

Is Supported: False

Description: N/A

Point set:

Is Supported: True

Description: The renderable point group contains a set of renderable point sets. Each renderable point set is associated with a different shader list in the shader group. The renderable point set consists of a vertex array. Each vertex in the vertex array contains all of the per vertex attributes (such as position, normal, texture coordinates, etc.) for that vertex. Each vertex in

the vertex array is drawn according to the parameters of the shaders in the shader list.

Mesh:

Manifold surface meshes:

Is Supported: False

Description: N/A

Manifold volume meshes:

Is Supported: False

Description: N/A

Non-manifold meshes:

Is Supported: False

Description: N/A

Parametric representation:

Parametric surfaces:

Is Supported: False

Description: N/A

Parametric curves:

Is Supported: False

Description: N/A

Contour sets:

Is Supported: False

Description: N/A

NURBS:

Is Supported: True

Description: This extension adds a Free-Form Surface Object to the U3D File Format specification that adds support for Uniform and Non-Uniform, Rational and Non-Rational Free-Form Curves and Surfaces.

Multi-resolution models:

Is Supported: True

Description: CLOD Description describes the range of resolutions available for the continuous level of detail mesh.

Dynamics:

Kinematics:

Is Supported: True

Description: Bone structure used in animation and inverse kinematics

Assembly:

Is Supported: False

Description: N/A

Force(s):

Is Supported: False

Description: N/A

Boundary representation

Manifold surface boundary representations:

Is Supported: False

Description: N/A

Manifold volume boundary representations:

Is Supported: False

Description: N/A

Non-manifold boundary representations:

Is Supported: False

Description: N/A

Material transparency:

Is Supported: True

Description: Opacity is a measure of on object’s transparency. The value is used when alpha blending. Higher Opacity means the object is less transparent and objects behind it will be less visible. The normal range of opacity is 0.0 (invisible) to 1.0 (completely opaque). Values outside this range are allowed.